HI Ben!
I hope you are well!  The question you ask is definitely not an easy one. As with seasons where you are, they can last different amounts of time every year and it is never something that can be accurately predicted.   Yurts book up very fast in the park, usually when the reservation system opens up 5 months before the booking date. So basically, if you are coming at a busy time or a weekend, you would most likely need to book the yurt 5 months before your planned arrival date to have the best chance of getting one.  With that said, there are lots of other options of places to stay while visiting the park, including, cabins, lodges, motels or even winter camping.
Last year we had snow well into April and the winter and snowfall we had was much less than the amounts we’ve received this season. With that being said, late March will most likely still be a great time for skiing and snowshoeing in the park, but again, it is not a guaranteed yes.
There are resources you can check online to assist you. One is at:  https://www.algonquinpark.on.ca/visit/recreational_activites/current-ski-trail-conditions.php  This site will give you the current ski trail conditions for the trails in the park and should help you with your questions.
This site may also assist in answering some of your questions:  https://www.algonquinpark.on.ca/visit/general_park_info/winter-in-algonquin-park.php
Regardless of the time of year you visit Algonquin Park, it is always a beautiful place with many things to see and do, and I hope you still visit and enjoy your time there!

– Christina

We’ve been in March and April for a few years.  One year it was mid 20 C and only snow banks could be found but the last 2 years there were still feet of snow and good snowshoeing conditions.  Camper Christina has given you some great information.